Differentiate between the principle of estimation of nitrogen in an organic compound by $(i)$ Dumas method and $(ii)$ Kjeldahl's method.

(N/A) In Dumas method,a known quantity of nitrogen-containing organic compound is heated strongly with excess of copper oxide $(CuO)$ in an atmosphere of carbon dioxide $(CO_2)$ to produce free nitrogen $(N_2)$ in addition to carbon dioxide and water. The chemical equation involved in the process is:
$C_xH_yN_z + (2x + y/2)CuO \to xCO_2 + y/2H_2O + z/2N_2 + (2x + y/2)Cu$
Traces of nitrogen oxides produced are reduced to dinitrogen by passing the mixture over a heated copper gauge. The $N_2$ gas is collected over an aqueous solution of potassium hydroxide $(KOH)$,and its volume is measured at room temperature and atmospheric pressure.
In Kjeldahl's method,a known quantity of organic compound is heated with concentrated sulphuric acid $(H_2SO_4)$. Nitrogen is quantitatively converted into ammonium sulphate $((NH_4)_2SO_4)$. This is then distilled with excess sodium hydroxide $(NaOH)$. The ammonia $(NH_3)$ evolved is passed into a known volume of $H_2SO_4$. The reactions are:
$Organic \text{ } compound \xrightarrow{Conc. H_2SO_4} (NH_4)_2SO_4$
$(NH_4)_2SO_4 + 2NaOH \to Na_2SO_4 + 2NH_3 + 2H_2O$
$2NH_3 + H_2SO_4 \to (NH_4)_2SO_4$
The unused acid is determined by titration against a standard alkali to calculate the amount of ammonia. This method is not applicable to compounds where nitrogen is in a ring structure or contains nitro $(-NO_2)$ or azo $(-N=N-)$ groups.